Heterologous production of methionine-gamma-lyase from Brevibacterium linens in Lactococcus lactis and formation of volatile sulfur compounds

Screening, characterization and anti-cancer application of purified intracellular MGL

L-methionine-γ-lyase (MGL) producing bacterial isolates were screened from soil samples that further characterized as 'Klebsiella oxytoca BLM-1' by biochemical and 16S rDNA sequencing. Intracellular MGL obtained from K. oxytoca BLM-1 by sonication was purified by Octyl-Sepharose and Sephadex G-200 column chromatography. MALDI-TOF-MS analysis of protein band (Mr ~ 63 kDa) confirmed the PLP-dependence and structural similarity with MGL enzyme. Purified MGL (1.1 μg) exhibited the maximum activity in potassium phosphate buffer (80 mM; with L-met 20 mM pH 7.0) at 37 °C. That further enhanced in the presence of NaCl (2 mM), Tween-80 (1.0 %; v/v) and EDTA (5 mM). K_m and V_max for purified MGL by using L-met as substrate was found to be 5.32 mM and 0.386 U/mL/min. The purified MGL showed PLP dependence and the half-life was 365.59 min. The MGL was effective against breast cancer (MCF7), gastric adenocarcinoma and human glioblastoma (U87MG) cancer cell lines with IC₅₀ values of purified MGL 0.041 U/mL, 0.008 U/mL and 0.009 U/mL, respectively. The U87MG, greatly affected by MGL treatment, when cultured in DMEM medium (10 mL) with PLP, homocysteine and 10 % FCS as compared to control/untransformed mouse spleen cells.

Sixty-One Volatiles Have Phylogenetic Signals Across Bacterial Domain and Fungal Kingdom

Microorganisms are diverse in their genome sequences and subsequently in their encoded metabolic pathways, which enabled them to adapt to numerous environmental conditions. They produce thousands of small molecules, many of which are volatiles in nature and play important roles in signaling in intra- and inter-species to kingdom and domain interactions, survival, or virulence. Many of these compounds have been studied, characterized, and organized in the mVOC 2.0 database. However, such dataset has not been investigated comprehensively in terms of its phylogeny to determine key volatile markers for certain taxa. It was hypothesized that some of the volatiles described in the mVOC 2.0 database could function as a phylogenetic signal since their production is conserved among certain taxa within the microbial evolutionary tree. Our meta-analysis revealed that some volatiles were produced by a large number of bacteria but not in fungal genera such as dimethyl disulfide, acetic acid, 2-nonanone, dimethyl trisulfide, 2-undecanone, isovaleric acid, 2-tridecanone, propanoic acid, and indole (common bacterial compounds). In contrast, 1-octen-3-ol, 3-octanone, and 2-pentylfuran (common fungal compounds) were produced primarily by fungal genera. Such chemical information was further confirmed by investigating genomic data of publicly available databases revealing that bacteria or fungi harbor gene families involved in these volatiles’ biosynthesis. Our phylogenetic signal testing identified 61 volatiles with a significant phylogenetic signal as demonstrated by phylogenetic D statistic P-value < 0.05. Thirty-three volatiles were phylogenetically conserved in the bacterial domain (e.g., cyclocitral) compared to 17 volatiles phylogenetically conserved in the fungal kingdom (e.g., aristolochene), whereas 11 volatiles were phylogenetically conserved in genera from both bacteria and fungi (e.g., geosmin). These volatiles belong to different chemical classes such as heterocyclic compounds, long-chain fatty acids, sesquiterpenoids, and aromatics. The performed approaches serve as a starting point to investigate less explored volatiles with potential roles in signaling, antimicrobial therapy, or diagnostics.

Mobilome of Brevibacterium aurantiacum Sheds Light on Its Genetic Diversity and Its Adaptation to Smear-Ripened Cheeses

Brevibacterium aurantiacum is an actinobacterium that confers key organoleptic properties to washed-rind cheeses during the ripening process. Although this industrially relevant species has been gaining an increasing attention in the past years, its genome plasticity is still understudied due to the unavailability of complete genomic sequences. To add insights on the mobilome of this group, we sequenced the complete genomes of five dairy Brevibacterium strains and one non-dairy strain using PacBio RSII. We performed phylogenetic and pan-genome analyses, including comparisons with other publicly available Brevibacterium genomic sequences. Our phylogenetic analysis revealed that these five dairy strains, previously identified as Brevibacterium linens, belong instead to the B. aurantiacum species. A high number of transposases and integrases were observed in the Brevibacterium spp. strains. In addition, we identified 14 and 12 new insertion sequences (IS) in B. aurantiacum and B. linens genomes, respectively. Several stretches of homologous DNA sequences were also found between B. aurantiacum and other cheese rind actinobacteria, suggesting horizontal gene transfer (HGT). A HGT region from an iRon Uptake/Siderophore Transport Island (RUSTI) and an iron uptake composite transposon were found in five B. aurantiacum genomes. These findings suggest that low iron availability in milk is a driving force in the adaptation of this bacterial species to this niche. Moreover, the exchange of iron uptake systems suggests cooperative evolution between cheese rind actinobacteria. We also demonstrated that the integrative and conjugative element BreLI (Brevibacterium Lanthipeptide Island) can excise from B. aurantiacum SMQ-1417 chromosome. Our comparative genomic analysis suggests that mobile genetic elements played an important role into the adaptation of B. aurantiacum to cheese ecosystems.

Effects of transgenic expression of Brevibacterium linens methionine gamma lyase (MGL) on accumulation of Tylenchulus semipenetrans and key aminoacid contents in Carrizo citrange

Carrizo transgenic plants overexpressing methionine-gamma-lyase produced dimethyl sulfide. The transgenic plants displayed more resistance to nematode attacks (Tylenculus semipenetrans) and may represent an innovative strategy for nematode control. Tylenchulus semipenetrans is a nematode pest of many citrus varieties that causes extensive damage to commercial crops worldwide. Carrizo citrange vr. (Citrus sinensis L. Usb × Poncirus trifoliate L. Raf) plants overexpressing Brevibacterium linens methionine-gamma-lyase (BlMGL) produced the sulfur volatile compound dimethyl sulfide (DMS). The aim of this work was to determine if transgenic citrus plants expressing BlMGL showed increased tolerance to T. semipenetrans infestation and to determine the effect on the content of key amino acids. While transgenic lines emitted dimethyl sulfide from leaves and roots, no sulfur-containing volatiles were detectable in wild-type Carrizo in the same tissues. Significant changes detected some key amino acids from leaves of transgenic plants such as aspartate, lysine, glycine, leucine and threonine with no changes in the amounts of methionine and α-ketobutyrate. In roots only glycine showed significant changes across all transgenic lines in comparison to wild-type plants. Transgenic plants expressing BlMGL and emitting DMS had less T. semipenetrans aggregation and more biomass than infected WT control plants, indicating that they may represent an innovative management alternative to pesticide/nematicide-based remedies.

Characterisation of the l-Cystine β-Lyase PatB from Phaeobacter inhibens: An Enzyme Involved in the Biosynthesis of the Marine Antibiotic Tropodithietic Acid

The l-cystine β-lyase from Phaeobacter inhibens is involved in the biosynthesis of the sulfur-containing antibiotic tropodithietic acid. The recombinant enzyme was obtained by heterologous expression in Escherichia coli and biochemically characterised by unambiguous chemical identification of the products formed from the substrate l-cystine, investigation of the substrate spectrum, determination of the enzyme kinetics, sequence alignment with closely related homologues and site-directed mutagenesis to identify a highly conserved lysine residue that is critical for functionality. PatB from P. inhibens is a new member of the small group of characterised l-cystine β-lyases and the first example of an enzyme with such an activity that is required for the biosynthesis of an antibiotic. A comparison of PatB to previously reported enzymes with l-cystine β-lyase activity from bacteria and plants is given.

l-Methioninase from some Streptomyces isolates I: Isolation, identification of best producers and some properties of the crude enzyme produced

Among 60 isolates of Streptomyces tested; only 40 isolates were capable to utilize l-methionine as the only source of nitrogen in medium. In addition, 24 of these isolates could grow in medium amended with l-methionine as a source of nitrogen and carbon. Qualitative rapid plate assay test shows the ability of 18 of these isolates to grow with a pink color surrounding their colonial growth, while 6 of these isolates could grow and utilize l-methionine without any pink color around their colonial growth. Quantitative assay test shows the rate of l-methioninase production by all isolates tested. Permeabilization treatment including chemical and physical methods proved that l-methioninase was found to be extracellularly produced. The results also indicate that l-methioninase production was not correlated with growth rate or l-methionine consumption in medium. On the other hand, quantitative assay test shows that these six isolates were l-methioninase negative and failed to produce any amount of l-methioninase. In addition, results also show that isolates No. 4 and No. 60 were the most suitable for l-methioninase production, these two isolates were characterized and identified as Streptomyces sp. DMMMH 4 and Streptomyces sp. MDMMH 60 using 16S rRNA with accession No. in gene bank. Furthermore, optimal conditions for enzyme activity produced by the two isolates were established in relation to temperature, pH, reaction time and type of buffer used and its molarities.

Purification, Characterization of L-Methioninase from Candida tropicalis, and Its Application as an Anticancer

The aim of the present study is to purify L-methioninase from Candida tropicalis 34.19-fold with 27.98% recovery after ion exchange chromatography followed by gel filtration. The purified enzyme revealed a single band on SDS-PAGE gel with a molecular weight of 46 KDa. Its optimum temperature was 45 to 55 and thermal stability was 55°C for 15 min. The enzyme had optimum pH at 6.5 and stability at a pH range of 5.5 to 7.0 for 24 hr. The maximum activity was observed with substrate concentration of 30 µM and Km was 0.5 mM. The enzyme was strongly inhibited by Cd(+2) and Cu(+2) while it was enhanced by Na(+), Ni(+2), and Mg(+2) at 10 mM while Ca(+2) had slight activation at 20 mM. In addition, the potential application of the L-methioninase as an anticancer agent against various types of tumor cell lines is discussed.

Metabolic fingerprint of dimethyl sulfone (DMSO2) in microbial-mammalian co-metabolism

There is growing awareness that intestinal microbiota alters the energy harvesting capacity of the host and regulates metabolism. It has been postulated that intestinal microbiota are able to degrade unabsorbed dietary components and transform xenobiotic compounds. The resulting microbial metabolites derived from the gastrointestinal tract can potentially enter the circulation system, which, in turn, affects host metabolism. Yet, the metabolic capacity of intestinal microbiota and its interaction with mammalian metabolism remains largely unexplored. Here, we review a metabolic pathway that integrates the microbial catabolism of methionine with mammalian metabolism of methanethiol (MT), dimethyl sulfide (DMS), and dimethyl sulfoxide (DMSO), which together provide evidence that supports the microbial origin of dimethyl sulfone (DMSO2) in the human metabolome. Understanding the pathway of DMSO2 co-metabolism expends our knowledge of microbial-derived metabolites and motivates future metabolomics-based studies on ascertaining the metabolic consequences of intestinal microbiota on human health, including detoxification processes and sulfur xenobiotic metabolism.

Methionine metabolism: major pathways and enzymes involved and strategies for control and diversification of volatile sulfur compounds in cheese

For economical reasons and to accommodate current market trends, cheese manufacturers and product developers are increasingly interested in controlling cheese flavor formation and developing new flavors. Due to their low detection threshold and diversity, volatile sulfur compounds (VSCs) are of prime importance in the overall flavor of cheese and make a significant contribution to their typical flavors. Thus, the control of VSCs formation offers considerable potential for industrial applications. This paper gives an overview of the main VSCs found in cheese, along with the major pathways and key enzymes leading to the formation of methanethiol from methionine, which is subsequently converted into other sulfur-bearing compounds. As these compounds arise primarily from methionine, the metabolism of this amino acid and its regulation is presented. Attention is focused in the enzymatic potential of lactic acid bacteria (LAB) that are widely used as starter and adjunct cultures in cheese-making. In view of industrial applications, different strategies such as the enhancement of the abilities of LAB to produce high amounts and diversity of VSCs are highlighted as the principal future research trend.

Exploring methionine γ-lyase structure-function relationship via microspectrophotometry and X-ray crystallography

Pyridoxal 5'-phosphate (PLP) dependent methionine γ-lyase catalyzes the breakdown of L-methionine to α-ketobutyric acid, methanethiol and ammonia. This enzyme, present in anaerobic microorganisms, has biomedical interest both for its activity as antitumor agent, depleting methionine supply in methionine-dependent cancers, and as target in the treatment of human pathogen infections, activating the pro-drug trifluoromethionine. To validate the structure of the enzyme from Citrobacter freundii, crystallized from monomethyl ether polyethylene glycol 2000, for the development of lead compounds, the reactivity of the crystalline enzyme towards L-methionine, substrate analogs and inhibitors was determined by polarized absorption microspectrophotometry. Spectral data were also collected for enzyme crystals, grown in monomethyl ether polyethylene glycol 2000 in the presence of ammonium sulfate. The three-dimensional structure of these enzyme crystals, solved at 1.65Å resolution with R(free) 23.2%, revealed the surprising absence of the aldimine bond between the active site Lys210 and PLP. Different hypothesis are proposed and discussed in the light of spectral and structural data, pointing out to the relevance of the complementarity between X-ray crystallography and single crystal spectroscopy for the understanding of biological mechanisms at molecular level. This article is part of a Special Issue entitled: Protein Structure and Function in the Crystalline State.